From Linear to Foldamer and Assembly: Hierarchical Transformation of a Coplanar Conjugated Polymer into a Microsphere

S Kushida and O Oki and H Saito and J Kuwabara and T Kanbara and M Tashiro and M Katouda and Y Imamura and Y Yamamoto, JOURNAL OF PHYSICAL CHEMISTRY LETTERS, 8, 4580-4586 (2017).

DOI: 10.1021/acs.jpclett.7b02102

Despite the coplanar structure, a conjugated alternating copolymer forms amorphous, well-defined microspheres without pi-stacked crystalline domains. Here, we gain insights into the mechanism of how the coplanar conjugated polymer forms amorphous microspheres by means of spectroscopic studies on the assembly/disassembly processes. The difference of the spectral profiles of photoabsorption and photoluminescence with varying solvent/nonsolvent composition clarifies that stepwise assembly takes place through the microsphere formation; 1 intrapolymer linear-to-folding transformation upon diffusion of polar nonsolvent and 2 interpolymer assembly of the foldamers upon further addition of the nonsolvent to form microspheres. As shown in various biopolymers such as proteins and DNA, such stepwise folding and assembly behaviors of conjugated polymers from primary to secondary and tertiary structure open a new way to create transformable functional materials.

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